Lamarck, the Founder of Evolution Part 30

"Besides, in reproductive unions the crossings between the individuals which have different qualities or forms are necessarily opposed to the continuous propagation of these qualities and these forms. We see that in man, who is exposed to so many diverse circ.u.mstances which exert an influence on him, the qualities or the accidental defects which he has been in the way of acquiring, are thus prevented from being preserved and propagated by generation.

If, when some particular features of form or any defects are acquired, two individuals under this condition should always pair, they would reproduce the same features, and the successive generations being confined to such unions, a special and distinct race would then be formed. But perpetual unions between individuals which do not have the same peculiarities of form would cause all the characteristics acquired by special circ.u.mstances to disappear.

"From this we can feel sure that if distances of habitation did not separate men the intermixture by generation would cause the general characteristics which distinguish the different nations to disappear.

"If I should choose to pa.s.s in review all the cla.s.ses, all the orders, all the genera, and all the species of animals which exist, I should show that the structure of individuals and their parts, their organs, their faculties, etc., etc., are in all cases the sole result of the circ.u.mstances in which each species is found to be subjected by nature and by the habits which the individuals which compose it have been obliged to contract, and which are only the product of a power primitively existing, which has forced the animals into their well-known habits.

"We know that the animal called the _ai_, or the sloth (_Bradypus tridactylus_), is throughout life in a condition so very feeble that it is very slow and limited in its movements, and that it walks on the ground with much difficulty. Its movements are so slow that it is thought that it cannot walk more than fifty steps in a day. It is also known that the structure of this animal is in direct relation with its feeble state or its inapt.i.tude for walking; and that should it desire to make any other movements than those which it is seen to make, it could not do it.

"Therefore, supposing that this animal had received from nature its well-known organization, it is said that this organization has forced it to adopt the habits and the miserable condition it is in.

"I am far from thinking so; because I am convinced that the habits which the individuals of the race of the _ai_ were originally compelled to contract have necessarily brought their organization into its actual state.

"Since continual exposure to dangers has at some time compelled the individuals of this species to take refuge in trees and to live in them permanently, and then feed on their leaves, it is evident that then they would give up making a mult.i.tude of movements that animals which live on the ground perform.

"All the needs of the _ai_ would then be reduced to seizing hold of the branches, to creeping along them or to drawing them in so as to reach the leaves, and then to remain on the tree in a kind of inaction, so as to prevent falling. Besides, this kind of sluggishness would be steadily provoked by the heat of the climate; for in warm-blooded animals the heat urges them rather to repose than to activity.

"Moreover, during a long period of time the individuals of the race of the _ai_ having preserved the habit of clinging to trees and of making only slow and slightly varied movements, just sufficient for their needs, their organization has gradually become adapted to their new habits, and from this it will result:

"1. That the arms of these animals making continual efforts readily to embrace the branches of trees, would become elongated;

"2. That the nails of their digits would acquire much length and a hooked shape, by the continued efforts of the animal to retain its hold;

"3. That their digits never having been trained to make special movements, would lose all mobility among themselves, would become united, and would only preserve the power of bending or of straightening out all together;

"4. That their thighs, continually embracing both the trunks and the larger branches of trees, would contract a condition of habitual separation which would tend to widen the pelvis and to cause the cotyloid cavities to be directed backward;

"5. Finally, that a great number of their bones would become fused, and hence several parts of their skeleton would a.s.sume an arrangement and a figure conformed to the habits of these animals, and contrary to what would be necessary for them to have for other habits.

"Indeed, this can never be denied, because, in fact, nature on a thousand other occasions shows us, in the power exercised by circ.u.mstances on habits, and in that of the influence of habits on forms, dispositions, and the proportion of the parts of animals, truly a.n.a.logous facts.

"A great number of citations being unnecessary, we now see to what the case under discussion is reduced.

"The fact is that divers animals have each, according to their genus and their species, special habits, and in all cases an organization which is perfectly adapted to these habits.

"From the consideration of this fact, it appears that we should be free to admit either one or the other of the following conclusions, and that only one of them is susceptible of proof.

"_Conclusion admitted up to this day_: Nature (or its Author), in creating the animals, has foreseen all the possible kinds of circ.u.mstances in which they should live, and has given to each species an unchanging organization, as also a form determinate and invariable in its different parts, which compels each species to live in the places and in the climate where we find it, and has there preserved its known habits.

"_My own conclusion_: Nature, in producing in succession every species of animal, and beginning with the least perfect or the simplest to end her work with the most perfect, has gradually complicated their structure; and these animals spreading generally throughout all the inhabitable regions of the globe, each species has received, through the influence of circ.u.mstances to which it has been exposed, the habits which we have observed, and the modifications in its organs which observation has shown us it possesses.

"The first of these two conclusions is that believed up to the present day--namely, that held by nearly every one; it implies, in each animal, an unchanging organization and parts which have never varied, and which will never vary; it implies also that the circ.u.mstances of the places which each species of animal inhabits will never vary in these localities; for should they vary, the same animals could not live there, and the possibility of discovering similar forms elsewhere, and of transporting them there, would be forbidden.

"The second conclusion is my own: it implies that, owing to the influence of circ.u.mstances on habits, and as the result of that of habits on the condition of the parts and even on that of the organization, each animal may receive in its parts and its organization, modifications susceptible of becoming very considerable, and of giving rise to the condition in which we find all animals.

"To maintain that this second conclusion is unfounded, it is necessary at first to prove that each point of the surface of the globe never varies in its nature, its aspect, its situation whether elevated or depressed, its climate, etc., etc.; and likewise to prove that any part of animals does not undergo, even at the end of a long period, any modification by changes of circ.u.mstances, and by the necessity which directs them to another kind of life and action than that which is habitual to them.

"Moreover, if a single fact shows that an animal for a long time under domestication differs from the wild form from which it has descended, and if in such a species in domesticity we find a great difference in conformation between the individuals submitted to such habits and those restricted to different habits, then it will be certain that the first conclusion does not conform to the laws of nature, and that, on the contrary, the second is perfectly in accord with them.

"Everything combines then to prove my a.s.sertion--namely, that it is not the form, either of the body or of its parts, which gives rise to habits, and to the mode of life among animals; but that it is on the contrary the habits, the manner of living, and all the other influencing circ.u.mstances which have, after a time, const.i.tuted the form of the body and of the parts of animals. With the new forms, new faculties have been acquired, and gradually nature has come to form the animals as we actually see them.

"Can there be in natural history a consideration more important, and to which we should give more attention, than that which I have just stated?

"We will end this first part with the principles and the exposition of the natural cla.s.sification of animals."

In the fourth chapter of the third part (vol. ii. pp. 276-301) Lamarck treats of the internal feelings of certain animals, which provoke wants (_besoins_). This is the subject which has elicited so much adverse criticism and ridicule, and has in many cases led to the wholesale rejection of all of Lamarck's views. It is generally a.s.sumed or stated by Lamarck's critics, who evidently did not read his book carefully, that while he claimed that the plants were evolved by the direct action of the physical factors, that in the case of all the animals the process was indirect. But this is not correct. He evidently, as we shall see, places the lowest animals, those without (or what he supposed to be without) a nervous system, in the same category as the plants. He distinctly states at the outset that only certain animals and man are endowed with this singular faculty, "which consists in being able to experience _internal emotions_ which provoke the wants and different external or internal causes, and which give birth to the power which enables them to perform different actions."

"The nervous fluid," he says, "can, then, undergo movements in certain parts of its ma.s.s, as well as in every part at once; moreover, it is these latter movements which const.i.tute the _general movements_ (_ebranlements_) of this fluid, and which we now proceed to consider.

"The general movements of the nervous fluid are of two kinds; namely,

"1. Partial movements (_ebranlements_), which finally become general and end in a reaction. It is the movements of this sort which produce feeling. We have treated of them in the third chapter.

"2. The movements which are general from the time they begin, and which form no reaction. It is these which const.i.tute internal emotions, and it is of them alone of which we shall treat.

"But previously, it is necessary to say a word regarding the _feeling of existence_, because this feeling is the source from which the inner emotions originate.

"_On the Feeling of Existence._

"The feeling of existence (_sentiment d'existence_), which I shall call _inner feeling_,[183] so as to separate from it the idea of a general condition (_generalite_) which it does not possess, since it is not common to all living beings and not even to all animals, is a very obscure feeling, with which are endowed those animals provided with a nervous system sufficiently developed to give them the faculty of feeling.

"This sentiment, very obscure as it is, is nevertheless very powerful, for it is the source of inner emotions which test (_eprouvent_) the individuals possessing it, and, as the result, this singular force urges these individuals to themselves produce the movements and the actions which their wants require. Moreover this feeling, considered as a very active _motor_, only acts thus by sending to the muscles which necessarily cause these movements and actions the nervous fluid which excites them....

"Indeed, as the result of organic or vital movements which are produced in every animal, that which possesses a nervous system sufficiently developed has physical sensibility and continually receives in every inner and sensitive part impressions which continually affect it, and which it feels in general without being able to distinguish any single one.

"The sentiment of existence [consciousness] is general, since almost every sensitive part of the body shares in it. 'It const.i.tutes this _me_ (_moi_) with which all animals, which are only sensitive, are penetrated, without perceiving it, but which those possessing a brain are able to notice, having the power of thought and of giving attention to it. Finally, it is in all the source of a power which is aroused by wants, which acts effectively only by emotion, and through which the movements and actions derive the force which produces them'....

"Finally, the inner feeling only manifests its power, and causes movements, when there exists a system for muscular movement, which is always dependent on the nervous system, and cannot take place without it."

The author then states that these emotions of the organic sense may operate in the animals and in man either without or with an act of their will.

"From what has been said, we cannot doubt but that the inner and general feeling which urges the animals possessing a nervous system fitted for feeling should be susceptible of being aroused by the causes which affect it; moreover, these causes are always the need both of satisfying hunger, of escaping dangers, of avoiding pain, of seeking pleasure, or that which is agreeable to the individual, etc.

"The emotions of the inner feeling can only be recognized by man, who alone pays attention to them, but he only perceives those which are strong, which excite his whole being, such as a view from a precipice, a tragic scene, etc."

Lamarck then divides the emotions into physical and moral, the latter arising from our ideas, thoughts--in short, our intellectual acts--in the account of which we need not follow him.

In the succeeding chapter (V.) the author dilates on the force which causes actions in animals. "We know," he says "that plants can satisfy their needs without moving, since they find their food in the environing _milieux_. But it is not the same with animals, which are obliged to move about to procure their sustenance. Moreover, most of them have other wants to satisfy, which require other kinds of movements and acts." This matter is discussed in the author's often leisurely and prolix way, with more or less repet.i.tion, which we will condense.

The lowest animals--those dest.i.tute of a nervous system--move in response to a stimulus from without. Nature has gradually created the different organs of animals, varying the structure and situation of these organs according to circ.u.mstances, and has progressively improved their powers. She has begun by borrowing from without, so to speak--from the environment--the _productive force_, both of organic movements and those of the external parts. "She has thus transported this force [the result of heat, electricity, and perhaps others (p. 307)] into the animal itself, and, finally, in the most perfect animals she has placed a great part of this force at their disposal, as I will soon show."

This force incessantly introduced into the lowest animals sets in motion the visible fluids of the body and excites the irritability of their contained parts, giving rise to different contractile movements which we observe; hence the appearance of an irresistible propensity (_penchant_) which constrains them to execute those movements which by their continuity or their repet.i.tion give rise to habits.

The most imperfect animals, such as the _Infusoria_, especially the monads, are nourished by absorption and by "an internal inhibition of absorbed matters." "They have," he says, "no power of seeking their food, they have not even the power of recognizing it, but they absorb it because it comes in contact with every side of them (_avec tous les points de leur individu_), and because the water in which they live furnishes it to them in sufficient abundance."

"These frail animals, in which the subtile fluids of the environing _milieux_ const.i.tute the stimulating cause of the o.r.g.a.s.m, of irritability and of organic movements, execute, as I have said, contractile movements which, provoked and varied without ceasing by this stimulating cause, facilitate and hasten the absorptions of which I have just spoken." ...